BOATS and STREAMS Q74

74.A man can row three-quarters of a kilometre against the stream in 11 minutes and down the stream in 7 minutes. The speed (in km/hr) of the man in still water is:

A.        2         B.        3

C.        4         D.        5

Answer: Option D

Explanation:

We can write three-quarters of a kilometre as 750 metres,

and 11  minutes as 675 seconds.

Rate upstream =		750	m/sec	=	10	m/sec.
		675			9

Rate downstream =		750	m/sec	=	5	m/sec.
		450			3

Rate in still water =	1		10	+	5	m/sec
	2		9		3

=	25	m/sec
	18

=		25	x	18	km/hr
		18		5

   = 5 km/hr.